Scaphoid Proximal Pole Fractures

Konstantinos N. Malizos, Zoe H. Dailiana, Sokratis E. Varitimidis

11.1 Introduction

Fractures of the proximal pole of the scaphoid are less common than those at the waist, but they attract particular attention because they usually present as occult fractures that are difficult to diagnose and whose configuration on plain radiographs is difficult to define.

Due to the precarious vascularity, they may develop avascular necrosis and the risk of nonunion remains high. According to Herbert’s classification, all proximal pole fractures (type B3), whether displaced or undisplaced, should be regarded as unstable. The characteristics of this particular fracture type are presented in combination with the particular problems and the complications in their management.^1,2

11.2 Anatomy

The name of the scaphoid bone comes from the Greek word “σκαφοειδές” (“skaphoedes”), indicating that the shape of the bone has been likened to the shape of a small boat or skiff.

The scaphoid is divided into the proximal pole, the waist, and the distal pole. The proximal pole articulates with the radius and lunate and the distal pole articulates with the capitate, trapezium, and trapezoid as far proximally as the palmar scaphoid tubercle. Heinzelmann et al,²⁰ using micro-computed tomography (micro-CT), found that the scaphoid bone is most dense at the proximal pole where the trabecular bone is thickest and more tightly packed. The trabeculae are thinnest and more sparsely distributed at the scaphoid waist, and this is where the majority of fractures occur.

Most of its surface (80–85%) is covered with articular cartilage. The predominantly articular nature of the scaphoid leaves little area for the entrance of blood vessels at the dorsal ridge of the bone. According to studies of Taleisnik and Kelly,²¹ and of Gelberman and Menon,²² the primary blood supply to the scaphoid is from the radial artery, through nutrient vessels from arches in the dorsoradial wrist capsule entering along the dorsal ridge of the scaphoid and providing 70% to 80% of its interosseous vascularity. Seventy to eighty percent of the vascularity of the entire proximal pole is from branches of the radial artery entering along the scaphoid waist. There is also a small vascular contribution via vessels entering the proximal pole along the fibers of the radioscapholunate ligament. The distal pole has additional blood supply, contributing the remaining 20% to 30%, from the superficial palmar branch that originates from the radial artery and perforates the scaphoid in the area of the scaphotrapezial ligament. This pattern of retrograde vascular anatomy of the scaphoid explains why proximally located fractures are associated with higher risk for nonunion and avascular necrosis.

11.3 Biomechanics

The scaphoid bone represents the osseous link that bridges the proximal and distal rows, thereby being subjected to continuous shearing and bending forces. In different populations undergoing wrist CT, it was found that the proximal pole was generally denser than the distal pole (proximal pole/distal pole ratio greater than 1), irrespectively of sex, age, or status of fracture.

A fracture of the scaphoid, as in the case of a fall on an outstretched hand, where the palmar aspect of the bone would fail in tension and the dorsal aspect in compression, results in abnormal load distribution about the wrist. Fractures of the proximal pole of the scaphoid are the result of dorsal subluxation during forced hyperextension. A complex combination of “bending” and “shearing” forces is acting to displace the scaphoid fracture fragments, depending on the location and the direction of the fracture plane, and the concomitant injuries of the wrist ligaments. When the fracture is left untreated it will commonly result in a DISI (dissociative intercalated segmental instability) deformity, as the proximal scaphoid fragment—anchored to the lunate through the intact scapholunate ligaments—turns in extension, while the distal scaphoid fragment—linked to the distal carpal row through a ligamentous network from the trapezium, trapezoid, and capitate—turns in flexion, resulting in a dorsal fracture gap. In simulated scaphoid fractures, it was demonstrated that opposing rotational moments on the proximal and distal poles caused dorsal angulation of the fractured scaphoid, the so-called “humpback” deformity. The “shearing” forces at the fracture site also translate the distal fragment laterally.³ This lateral translation of the distal fragment leads to abnormal loading on the radial styloid and arthritis is gradually established. The term SNAC (scaphoid nonunion advanced collapse) wrist was coined after the identification of the predictable and time-dependent development of arthritis in scaphoid nonunions.

11.4 Assessment and Diagnosis

Scaphoid fractures at the proximal half of the bone often occur with minimal symptoms in a young and active population and a high index of suspicion is necessary not to miss the diagnosis. The examination of a patient with an acute fracture will reveal tenderness on palpation in the anatomical snuffbox, volar pain on palpation of the distal tuberosity, pain on axial compression of the thumb metacarpal (scaphoid compression test), decreased range of motion, and swelling.

High-quality radiographs should include (as a minimum) the following views: anteroposterior, lateral, posteroanterior with ulnar deviation, and oblique with 45° of pronation. When a fracture is suspected, but cannot be demonstrated on these initial radiographs, the examiner should always avoid the diagnosis of a “wrist sprain.” If available, an ultrasound examination can evaluate the presence of a cortical interruption of the scaphoid along with a radiocarpal or scapho-trapezium-trapezoid effusion. Ultrasonography could be used on a routine basis in emergency settings for the triage to CT in patients with clinical suspicion of scaphoid fracture and normal radiographs. CT scan is the most suitable technique for the diagnosis, with 0.5- to 1-mm sagittal sections taken in the plane of the scaphoid. In the presence of a fracture, CT is the best tool for assessing the fracture location, comminution, and deformity, thus facilitating treatment selection. Magnetic resonance imaging (MRI), however, is the most reliable modality for diagnosing acute and occult fractures and can reveal a scaphoid fracture within 24 hours from the injury.⁴

11.5 Management of Acute Proximal Pole Fractures

Both displaced and nondisplaced fractures of the proximal pole are considered unstable. Herbert and Fisher classified proximal pole fracture of the scaphoid as type B3 (all type B fractures are considered unstable), whereas Cooney et al defined several fracture patterns as unstable and among them are the proximal pole fractures.^1,5

There are several reasons why proximal pole fractures have high rates of nonunion and avascular necrosis. Due to the small size of the proximal fragment and the tenuous blood supply, the fracture cannot be completely immobilized in order to optimize the conditions for revascularization and healing. The proximal location of the fracture leads to large lever-arm stress across the fracture site and nonoperative management with casting cannot achieve the optimal conditions for fracture healing. In addition, due to its intra-articular location, the synovial fluid can block the fracture-healing process.⁶

Although some authors believe that nondisplaced fractures of the proximal pole can be managed nonoperatively, through the application of a cast for a period of approximately 4 months (long arm cast for 6 weeks, followed by short arm cast for at least 2 months), the majority of experts believe that for proximal pole fractures internal fixation is the treatment of choice due to the inherent instability, the prolonged time to healing, and the high rates of nonunion.² Studies comparing the operative versus nonoperative treatments of proximal pole fractures found significantly higher union rates in the operative groups, especially for the displaced fractures, although significantly higher rates of complications were also noted in the operative groups.

11.5.1 Surgical Management

There is a consensus that the fractures of the proximal pole of the scaphoid as well as the respective nonunions should be treated operatively with internal fixation through an intraosseous fixation device appropriate for the small size of the proximal fragment. For proximal pole fractures the surgical treatment alternatives include an open, mini-open, or percutaneous technique (with or without arthroscopic assistance).^6,7,8 The use of percutaneous fixation is limited to undisplaced fractures and is based on cannulated screw fixation devices. Although it is believed that percutaneous fixation shortens the duration of immobilization, and provides higher rates of union, it was found that the open technique is superior to the percutaneous in achieving union in scaphoid fractures. According to Krimmer, the open approach does not incise any ligaments and avoids the risk of incorrect positioning of the screw that percutaneous fixation has.²

Open Technique

Dorsal surgical approach The dorsal surgical approach allows visualization of the proximal scaphoid and of the scapholunate ligament and simplifies the insertion of the screw in addition to leaving intact the volar carpal ligaments. The incision is centered over the Lister tubercle and may be longitudinal or transverse. After retraction of the extensor pollicis longus tendon and incision of the capsule in line with the Lister tubercle, the scapholunate interval is exposed with care for the scapholunate ligament. The surgical approach through partial opening of the second and third extensor compartments and the wrist capsule does not compromise the blood supply any further and provides limited but adequate and safe access to the proximal fragment. It allows clear visualization of the fracture and exact placement of the entry point for the guidewire, minimizing the increased risk of incorrect positioning of the screw with the closed technique and the disruption of the proximal fragment.⁶

Intraoperatively, the surgeon must accomplish an anatomical reduction and secure a rigid fixation, able to resist the complex forces of normal functional loading of the wrist, taking into consideration the quality of the bone and the geometry of the fracture. Two more crucial parameters for a successful outcome are selection of the appropriate implant and its placement in the biomechanically ideal position for the individual patient and the specific fracture pattern. The bone density is greatest in the scaphoid poles, providing the best fixation. A long headless screw from proximal to distal, spanning the entire scaphoid, reduces the forces at the fracture site.

The size of the proximal pole segment can pose additional difficulty for rigid fixation, which might be even worse in the case of a proximal pole nonunion with a bone graft. In such cases a supplemental fixation is commonly applied from the distal scaphoid to the capitate, or even better to the lunate, using a 1.2-mm K-wire. The advantage of the latter is the indirect stabilization through the intact scapholunate ligaments and the protection of the small and fragile proximal pole fragment from repeated attempts to find optimal implant placement.

A below-elbow cast is applied postoperatively for wrist immobilization for 2 weeks and heavy manual activity is restricted during the first 6 weeks.